In-Situ Laser Cladding of Al2O3 Reaction Coating on Aluminium Alloy 7075 for Corrosion Resistance Improvement

The microstructure and corrosion behaviour of the thermite reaction coatings for the systems of Al-CuO-SiO2, Al-Cr2O3-SiO2, and Al-TiO2-SiO2 that produced by laser cladding on aluminium alloy 7075 have been studied. The results of the XRD analysis show that in all the three reaction coatings, (alpha)-Al2O3 and (gamma)-Al2O3 phases were present together with various intermetallic phases and the corresponding reduced metal. A comparison of the polarisation curves of the untreated and the various coated specimens shows that except for the Al-CuO-SiO2 system, the corrosion current density of the coated specimens was one order of magnitude lower than that of the untreated specimen, also a higher corrosion potential was obtained. The inferior corrosion resistance of the Al-CuO-SiO2 system is attributed to galvanic corrosion occurred between the reduced metal, the intermetallic compounds and aluminium.